Patrick Preissler, Technische Universität München, Freising, Germany
Co-author(s): Jürgen Behr and Rudi Vogel, Technische Universität München, Freising, Germany
ABSTRACT: Manganese is an essential metal for lactic acid bacteria, which is part of many enzymes, often replacing (redox) functions of iron in enzymes of other bacteria. As bacteria lack compartmentation, metal ion homeostasis is maintained primarily by regulation of metal cation flux across the cell membrane. It has been shown that hop compounds induce efflux of manganese, which is part of bacterial stress response and adaptation to iso-alpha-acids. On the other hand, the permeability of the membrane is adjusted through its membrane lipid composition, which may influence (manganese) transporter effectiveness and also intrusion of weak acids and other antibiotic compounds. As a result, a decrease in membrane fluidity could contribute to hop tolerance and beer-spoiling ability. In this study, we have investigated the influence of initial intracellular manganese levels and incubation in lager beer on the effects of metal trace elements and the composition of fatty acids in the cell membrane. Cells of beer-spoiling Lactobacillus brevis TMW 1.313 exhibited reduction of manganese and decreasing zinc concentrations after adaptation to the beer environment. At the same time, intracellular calcium, iron, and magnesium levels were increased. The analysis of cytoplasmic fatty acids composition showed that adaptation to beer after 5 days of incubation resulted in a reduction of the amounts of saturated fatty acids 12:0 and 16:0 3OH, whereas those of the two cyclic fatty acids (17:0 and 19:0), as well as the saturated fatty acid 18:0 and the unsaturated 20:2 ,were increased in the cell membrane. In conclusion, both tuning of the membrane composition and balanced metal ion content contributed to improved survival of L. brevis in beer by reduction of hop sensitivity and concomitant acid stress. This may indicate that functionality of metal ion transporters is modulated in such a membrane and both traits are connected.
Patrick Preissler was born in 1981 in Erfurt, the regional capital of Thuringia. He studied nutrition science at Friedrich-Schiller-Universität in Jena. In 2011 he finished his Ph.D. thesis on mechanisms of hop tolerance in beer-spoiling Lactobacillus brevis at Technische Universität München under the supervision of Rudi F. Vogel at the Chair of Technische Mikrobiologie in Weihenstephan.
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